Various hydrocarbon feedstocks such as crude petroleum oils, topped crudes, heavy vacuum gas oils, shale oils, tar sand bitumens, and other heavy hydrocarbon fractions such as residual fractions and distillates contain varying amounts of non-metallic and metallic impurities. The non-metallic impurities include nitrogen, sulfur, and oxygen and these exist in the form of various compounds and are often in relatively large quantities. The most common metallic impurities include iron, nickel, and vanadium. Other metallic impurities including copper, zinc, and sodium are often found in various hydrocarbon feedstocks and in widely varying amounts. The metallic impurities may occur in several different forms as metal oxides or sulfides which are easily removed by simple processing techniques such as by filtration or by water washing. However, the metal contaminants also occur in the form of relatively thermally stable organo-metallic complexes such as metal porphyrins.
Residual petroleum oil fractions produced by atmospheric or vacuum distillation of crude petroleum are characterized by relatively high metals and sulfur content. This occurs because substantially all of the metals present in the original crude remain in the residual fraction, and a disproportionate amount of sulfur in the original crude oil also remains in that fraction.
The high metals content of the residual fractions generally preclude their effective use as charge stocks for subsequent catalytic processing such as catalytic cracking and hydrocracking, because the metal contaminants deposit on the special catalysts for these processes and cause the formation of inordinate amounts of coke, dry gas and hydrogen.
It is current practice to upgrade certain residual fractions by a pyrolitic operation known as coking. In this operation the residuum is destructively distilled to produce distillates of low metals content and leave behind a solid coke fraction that contains most of the metals. Coking is typically carried out in a reactor or drum operated at about 800.degree.-1100.degree. F. temperature and a pressure of 1-10 atmospheres. The economic value of the coke byproduct is determined by its quality, particularly its sulfur and metals content. Excessively high levels of these contaminants makes the coke useful only as low-valued fuel. In contrast, cokes of low metals content, for example up to about 100 ppm (parts per million by weight) of nickel and vanadium, and containing less than about 2 weight percent sulfur may be used in high-valued metallurgical, electrical, and mechanical applications.
Certain residual fractions are currently subjected to visbreaking, which is a heat treatment of milder conditions than used in coking, in order to reduce their viscosity and make them more suitable as fuels. Again, excessive sulfur content sometimes limits the value of the product.
Presently, catalytic cracking is generally accomplished by utilizing hydrocarbon charge stocks lighter than residual fractions which usually have an API gravity less than 20. Typical cracking charge stocks are coker and/or crude unit gas oils, vacuum tower overhead, and the like, the feedstock having an API gravity from about 15 to about 45. Since these cracking charge stocks are distillates, they do not contain significant proportions of the large molecules in which the metals are concentrated. Such cracking is commonly carried out in a reactor operated at a temperature of about 800.degree.-1500.degree. F., a pressure of about 1-5 atmospheres, and a space velocity of about 1-1000 WHSV.
Conventionally, a distillate feedstock contains low metals contents (less than 100 ppm) and is considered particularly suitable for catalytic cracking.
The residual fractions of typical crudes will require treatment to reduce the metals contents. As almost all of the metals are combined with the residual fraction of a crude stock, at least about 80 percent of the metals and preferably at least 90 percent needs to be removed to produce fractions suitable for cracking charge stocks. As an example, a typical Arabian residue, considered of average metals content, contains 68 ppm vanadium and 17 ppm nickel.
Metals and sulfur contaminants present similar problems with regard to hydrocracking operations which are typically carried out on feedstocks even lighter than those charged to a cracking unit. Hydrocracking catalyst is so sensitive to metals poisoning that a preliminary or first stage is often utilized for trace metals removal. Typical hydrocracking reactor conditions consist of a temperature of 400.degree.-1000.degree. F. and a pressure of 100-3500 psig.
The economic and environmental factors relating to upgrading of petroleum residual oils and other heavy hydrocarbon feedstocks have encouraged efforts to provide improved processing technology, as exemplified by the disclosures of various United States patents.
U.S. Pat. No. 3,716,479 describes a process for the demetalation of a hydrocarbon charge stock containing metal impurities which involves contacting the hydrocarbon charge stock with hydrogen and with a catalyst comprising the naturally-occurring underwater deposit known as manganese nodules.
U.S. Pat. No. 3,839,187 describes a process for removing metal contaminants from a petroleum residual oil without significant coking and loss of hydrocarbons by treating such oils with a hydrogen donor solvent in the presence of a highly porous inorganic scrubbing agent such as clay, and recycling the regenerated metal-containing scrubbing agent.
U.S. Pat. No. 3,847,798 discloses a means for reducing the sulfur content of hydrocarbon material by oxidizing the sulfur impurities contained in the hydrocarbon material and then contacting the oxidized sulfur-containing hydrocarbon material with at least one hydrocarbon hydrogen donor component capable of transferring hydrogen under conditions such that hydrogen transfer from said component to the oxidized sulfur-containing hydrocarbon material occurs.
U.S. Pat. No. 3,901,792 describes a multi-zone method for demetalizing and desulfurizing crude oil or atmospheric residual oil. An initial contact stage contains a material having extensive macroporosity and is operated as an ebullated bed under optimum demetalation conditions. This is followed by a removal of effluent vapors and a further ebullated bed contact of the liquid with a highly active hydrodesulfurization catalyst.
U.S. Pat. No. 3,905,893 discloses a hydrodesulfurization and demetalation process which involves an initial stage having relatively high hydrogen pressure in the presence of a catalyst comprising a relatively low proportion of catalytically active hydrogenation metals. The process employs a final stage in series having a relatively lower hydrogen pressure and a catalyst comprising a relatively higher proportion of hydrogenation metals.
U.S. Pat. No. 3,936,371 discloses a method for removing vanadium, nickel, sulfur and asphaltenes from hydrocarbon oils which involves contacting the hydrocarbon oil with red mud having from 18-25 percent by weight aluminum oxide, 15-20 percent by weight silicon dioxide, 30-40 percent by weight ferric oxide, 2-8 percent by weight titanium dioxide, and 8-12 percent by weight of matter that is lost by ignition, at elevated temperatures and in the presence of hydrogen.
U.S. Pat. No. 3,964,995 discloses a two-stage hydrodesulfurization process for a 65-80 percent desulfurization of a high metals content residuum. The first stage contains porous alumina contact material activated with at least one promoter oxide. The second stage contains a highly active desulfurization catalyst of limited porosity.
U.S. Pat. No. 3,985,643 describes an improved process for desulfurization of metals and sulfur-containing petroleum oils, which involves passing a petroleum oil through a bed of substantially aged desulfurization catalyst at a temperature not less than 770.degree. F. preceeding conventional hydrodesulfurization treatment.
Other United States patents which relate to desulfurization, demetalation and denitrification of heavy hydrocarbon oils include U.S. Pat. Nos. 2,591,525; 2,761,816; 2,909,476; 2,921,022; 2,950,231; 2,987,470; 3,094,480; 3,594,312; 3,663,434; 3,676,369; 3,696,027; 3,766,054; 3,772,185; 3,775,303; 3,813,331; 3,876,530; 3,882,049; 3,897,329; and the like, and references cited therein.
There is continuing research effort to improve the efficiency of processing means for upgrading of hydrocarbon feedstocks, with particular reference to petroleum residual oils.
Accordingly, it is an object of this invention to provide an improved catalytic process for reducing the sulfur, metal and nitrogen content of hydrocarbon oils.
It is another object of this invention to provide a process for upgrading heavy hydrocarbon feedstocks, in the presence of a relatively inexpensive catalyst and without the addition of hydrogen gas.
Other objects and advantages of the present invention shall become apparent from the accompanying description and illustrated data.